Process for removing cluster adhering to cathode during electrolysis of manganous sulfate

ABSTRACT

Cluster formed on and adhering to a cathode during electrolysis of manganous sulfate solution containing calcium sulfate and magnesium sulfate in the production of electrolytic manganese dioxide is easily removed without injury to the cathode by newly effecting electrolysis but using the cathode as an anode to deposit manganese dioxide thereon and giving an impact to the depositied manganese dioxide to peel off the cluster together therewith.

United States Patent [191 Kosaka [4 1 Dec. 17,1974

PROCESS FOR REMOVING CLUSTER ADHERING TO CATHODE DURING ELECTROLYSIS OF MANGANOUS SULFATE [75] Inventor: Tetsuji Kosaka, Takehara, Japan [73] Assignee: Mitsui Mining & Smelting, Co.,

Ltd., Tokyo, Japan [22] Filed: Aug. 27, 1973 [21] Appl. No.: 391,804

[52] US. Cl 204/96, 204/10, 204/57, 204/281 [51] Int. Cl C0lb 13/14 [58] Field of Search 204/57, 96, 10, 281

[56] References Cited UNITED STATES PATENTS 3,065,155 11/1962 Welsh 204/96 3,455,81 l 7/1969 Bender et a1. 204/281 Primary ExaminerJohn H. Mack Assistant ExaminerR. L. Andrews Attorney, Agent, or Firm-Armstrong, Nikaido & Wegner [5 7] ABSTRACT 7 pact to the depositied manganese dioxide to peel off the cluster together therewith.

- 5 Claims, No Drawings PROCESS FOR REMOVING CLUSTER ADHERING TO CATHODE DURING ELECTROLYSIS OF MANGANOUS SULFATE This invention relates to removal of cluster formed during electrolysis on the surface of a cathode in the production of electrolytic manganese dioxide by electrolysis using as an electrolyte an aqueous sulfuric acid manganous sulfate solution by the use of electrodes insoluble in the electrolyte.

ln electrolytically producing manganese dioxide, materials insoluble in an electrolyte are used as electrodes. Generally speaking, there are usually employed lead, lead alloys or graphite for cathode, and lead or lead alloys, carbon or titanium for anode. ln the production of electrolytic manganese dioxide, particularly in the process step of electrolysis, there are adopted, for example, such conditions that an anode current density is 0.6-1.2 A/dm an electrolyte temperature is 8595C, amounts of manganese and sulfuric acid are 10-60 g/l and 20-100 g/l, respectively. An anode is pulled up from the electrolyser every 10 to 40 days, and the manganese dioxide block deposited electrolytically on the anode is peeled off by means of a suitable procedure, for example, by giving a slight impact to the block. The anode is then cleaned by washing and returned again back to the electrolysis process step. On the other hand, a cathode is used continuously while being immersed and maintained in the electrolyte. However, when concentrations of sulfates of the alkali earth metals dissolved in the electrolyte, such as calcium or magnesium, exceed their solubilities in said electrolyte with the progress of electrolysis, the sulfates come to adhere to the surface of cathode to form a so-called cluster rigidly adhered thereto.

The alkaline earth metals such as calcium and magnesium are originally contained as impurities in the starting manganese ore, and extracted in the form of sulfates therefrom with an aqueous sulfuric acid solution or spent electrolyte in the preparation of a replenishing neutral aqueous manganous sulfate solution for consumed manganese in electrolyte. Further, the replenishing manganous sulfate solution comes to be contaminated with calcium sulfate when the extract of the manganese ore is neutralized with calcium salts such as calcium carbonate and calcium hydroxide. if the electrolysis is continued while using a cathode having cluster adhering thereto, as it is, ununiform current is caused and, as the result, invites the increase of electrolyte voltage and lowering of current efficiency, which results in remarkable increase of overall power required. Further, the ununiform current influences an anode and shortens its life. Accordingly, the continued operation of electrolysis is usually suspended every 5 to 6 months. After suspension of the operation, there is need for such labor that the cathode is pulled up from the electrolyser, the electrode system is disintegrated, the cluster adhering to the cathode is permitted by giving a compact thereto for example, with a hammer to fall down therefrom, and the surface of the cathode is then subjected to smoothening operation by means of sand brushing or the like. Furthermore, not only the cluster adheres closely to the cathode and is difficult to remove but also the cathode is damaged in many cases during the removal operation of the cluster when the material of the electrode is selected from such one as graphite which is mechanically fragile, and this causes wear of the electrode to a large extent. There has also beenproposed a process of chemically removing cluster from cathode, for example, by treating the cluster with hydrochloric acid to allow said cluster to dissolve in the acid, thereby removing the cluster from the cathode. In this process, however, it takes a long period of time to dissolve the cluster in the acid and, in addition, electrodes may suffer from corrosion with the acid when they are made of metallic materials.

An object of the present invention is to provide a process for removing cluster from cathode in which a labor for removal of the cluster may be decreased and the electrodes may be freed from damage and corrosion.

The present inventors conducted extensive studies and have found that when an electrolysis of the electrolyte is conducted anew by use of the cathode to which the cluster has adhered as an anode, that is, when the electrolysis is conducted exchanging the electrodes each other, the deposition of manganese dioxide occurs on the cluter which can be readily removed together with the manganese dioxide having been deposited from the anode which has been used formerly as a cathode.

That is, the present invention is to provide a process for removing from a cathode'a cluster formed oh and adhered to the surface of the cathode during electrolysis of an aqueous sulfuric acid-manganous sulfate solution containing alkali earth metal sulfates for the production of electrolytic manganesedioxide, said cluster being composed mainly of the alkaline earth metal salts, which process is characterized by carrying out said electrolysis using the cathode having said cluster firmly adhered to the surface thereof as an anode, electrolytically depositing manganese dioxide on said cluster, and peeling off said cluster together with the electrolytically deposited manganese dioxide by giving a compact to said deposited manganese dioxide.

Formation ofthe cluster on a cathode during the production of electrolytic manganese dioxide is considered ascribable to the fact that the aforesaid neutral aqueous manganous sulfate solution is replenished at 50 to 60C, and the electrolyte is maintained at a high temperature such as to C as mentioned previously, and, on the other hand, solubilities of the sulfates such as CaSO, and MgSO, contained in the electrolyte decrease with the increase of temperature, thus the solubilities are inversely relative to the temperature, and hence the sulfates deposit on the cathode when the concentrations of calcium and magnesium become 0.10-0.50 g/l and 20-60 g/e, respectively. When an aqueous sulfuric acid-manganous sulfate solution is electrolyzed under common electrolysis conditions as mentioned previously using a cathode having a cluster deposited thereon as an anode, while using a cathode made of the same or different material, manganese dioxide deposits on the anode having the cluster deposited thereon. In this case, it is considered that the deposited manganese dioxide permeates into crystal lattices of CaSO, and the like, which constitute the cluster, thereby deteriorating the adhesion of crystals of CaSO, and the like to'the electrode, and hence the cluster comes to peel off more readily therefrom. The electrolysis time employed in the above case is, in short, a minimum time required for attaining a state where the cluster comes to readily peel off together with the manganese dioxide deposited thereon, and such electrolysis time may be experimentally decided.

For example, under the electrolysis conditions referred to previously, the electrolysis time is usually 3 to 10 hours, preferably about hours. By conducting such an electrolysis as in changing electrodes formerly used in merely given as illustrative and the invention is not limited only thereto.

EXAMPLE Electrolysis of an aqueous sulfuric acid-manganous accordance with the present invention, a cluster ad- 5 sulfate solution containing calcium and magnesium sulheredto the surface of a graphite or carbon cathode fates was carried out for 5 hours using as an anode a can be removed together with the manganese dioxide Carbon ou bar of 33 mm in diameter and l,l00 mm formerly deposited thereon without injury to the cathin length which has been already used as a Cathode ih d b i i h a li h impact as may b n the preceding electrolysis for six months and, as a regiven to manganese dioxide deposited on an anode in sult, which has on its surface a cluster layer of 2.16 mm a conventional manner in thickness, and as a cathode a carbon round bar hav- The electrolyte used in the practice of the invention ing the same dimention as in said anode but free from may be any aqueous solution for electrolysis so long as Clusterit contains sulfuric acid and manganous sulfate. When, The electrolysis Conditions were Slime as iii the P however, an electrolyte which h b l d d i ceeding electrolysis and such that an electrolyte conthe preceding electrolysis and which contains calcium in ng 25 g/ of Mn, 5 g/ of 2 4, 36 g/l of Mg and magnesium salts is used, the object of the invention and 8 of eeieiiim++ was used, the temperature of may be conveniently accomplished b m r l ch i the electrolyte was maintained at 90C., and the anode' the electrodes or shunting the negative and positive current density was 0.8 A/dm currents employed in the preceding electrolysis operahen a rl l'mal impact was gi n t the manganese tion. dioxide electrolytically deposited on the surface of the In accordance with the present invention, there are cluster adhering to the anode, the cluster was readily brought about such marked effects that labor in treatremoved together with the deposited manganese dioxing a cathode for removing cluster in the conventional ide from said anode. The results of assay of the cluster process can be sharply reduced and the wearing-out of before and after the electrolysis are given in the followthe cathode in use is markedly reduced. The present ing table- ('70) Total Soluble M110 Ca Mg SiO: SO, H O Pccling property Mn Mn Cluster before i 6.0 6.0 9.2 l7.8 2.4 O.ll 6L4 l.0 Difficult electrolysis Cluster after 22.5 2.9 2|.6 1 L6 3.6 0.02 37.2 4.7 Good electrolysis process may also be applicable to the case where man- The anode, from the surface of which the deposited ganese dioxide is produced by electrolysis using metalmanganese dioxide and adhered cluster had been relic materials such as lead and/or lead alloys are used for moved in the manner as mentioned above was used, as an anode and a cathode, respectively, or for both. How- 40 it was, as a cathode in the subsequent electrolysis operever, the process is most preferably applied to the case ation without any difficulty. And, the cluster thus rewhere a graphite or carbon cathode is used, wher by moved was mixed with a starting manganese ore and particularly marked results can be obtained. used in the step of preparing a fresh electrolyte.

As a secondary effect of the process of the present hat iS aimed SI invention when a fresh graphite material is used as an A pr r ng lust r prising alkaline anode, there may be brought about s ch advantag as earth metal sulfates, which cluster is deposited on a mentioned below. That is, the fresh graphite material cathode during electrolysis of an aqueous sulfuric acidhas a conductivity better than the graphite material manganous sulfate solution containing the alkali earth once used as an anode, and hence th mang n di metal salts in the production of electrolytic manganese ide deposited thereon becomes difficult t b v d dioxide, which process comprises effecting the electroltherefrom because the dioxide compactly deposits on y of an aqueous Sulfuric acid-manganous Sulfate the surface of said fresh graphite anode, thus removal iiitioh y use of the Cathode having the cluster p of the deposited man dio id f h f h ited on its surface as an anode to deposit the electrographite anode frequently tends to do damage to the lytic manganese dioxide on the cluster, and giving an anode. 1n the above case, th r f wh th f h impact to the deposited manganese dioxide so that the graphite anode is first used as a cathode and a cluster cluster is peeled Off together with the manganese tiiOX- is allowed to deposit on the cathode and, thereafter, the cluster is removed together with the manganese dioxide A PieceSS according to Claim wherein the Cathdeposited thereon according to the present process as Ode having the Cluster deposited thereon is made of mentioned previously, and the cathode from the surgraphite 0r Carbon face of which the cluster has been removed is then used A Process according t0 Claim wherein the elecanew as an anode, the wearing-out of the anode after troiysis is effected at a temperature of to the treatment as mentioned above is thusreduced from under a Current density of to L2 A/(lm2 at the an overall point of view because the deposited manga- 65 nese dioxide easily comes off therefrom.

The present invention is illustrated below in further detail with reference to an example. but the example is 4. A process according to claim 1, wherein the aqueous sulfuric acid-manganous sulfate solution containing the alkaline earth metal salts comprises 10-60 g/l of manganese, -100 g/l of sulfuric acid, 0.10-0.50 g/l of the electrolysis by the use of the cathode having the calcium and 20-60 g/l of magnesium.

cluster deposited thereon as an anode contains the al- 5. A process according to claim 1, wherein the aquekaline earth metal salts. ous sulfuric acid-manganous sulfate solution used in 

1. A PROCESS FOR REMOVING CLUSTER COMPRISING ALKALINE EARTH METAL SULFATES, WHICH CLUSTER IS DEPOSITED ON A CATHODE DURING ELECTROLYSIS OF AN AQUEOUS SULFURIC ACID-MANGANOUS SULFATE SOLUTION CONTAINING THE ALKALI EARTH METAL SALTS IN THE PRODUCTION OF ELECTROLYTIC MANGANESE DIOXIDE, WHICH PROCESS COMPRISES EFFECTING THE ELECTROLYSIS OF AN AQUEOUS SULFURIC ACIDMANGANOUS SULFATE SOLUTION BY USE OF THE CATHODE HAVING THE CLUSTER DEPOSITED ON ITS SURFACE AS AN ANODE TO DEPOSIT THE ELECTROLYTIC MANGANESE DIOXIDE ON THE CLUSTER, AND GIVING AN IMPACT TO THE DEPOSITED MANGANESE DIOXIDE SO THAT THE CLUSTER IS PEELED OFF TOGETHER WITH THE MANGANESE DIOXIDE.
 2. A process according to claim 1, wherein the cathode having the cluster deposited thereon is made of graphite or carbon.
 3. A process according to claim 1, wherein the electrolysis is effected at a temperature of 85* to 95*C under a current density of 0.6 to 1.2 A/dm2 at the anode.
 4. A process according to claim 1, wherein the aqueous sulfuric acid-manganous sulfate solution containing the alkaline earth metal salts comprises 10-60 g/l of manganese, 20-100 g/l of sulfuric acid, 0.10-0.50 g/l of calcium and 20-60 g/l of magnesium.
 5. A process according to claim 1, wherein the aqueous sulfuric acid-manganous sulfate solution used in the electrolysis by the use of the cathode having the cluster deposited thereon as an anode contains the alkaline earth metal salts. 